Driver side or passenger side passive inflatable restraint (PIR) systems typically include an air bag stored in a housing module within the interior of the vehicle in close proximity to either the driver or one or more passengers. PIR systems are designed to actuate upon sudden deceleration so as to rapidly deploy an air bag to help restrain the movement of the driver or passengers. During deployment, gas is emitted rapidly from an inflator into the air bag to expand it to a fully inflated state.
Air bag passive restraint systems include an inflator, which produces gas to inflate an air bag cushion. There are several types of inflators for air bag modules. One type is the cold gas inflator wherein a pressure vessel contains stored pressurized gas. The pressure vessel communicates with the cushion through various types of rupturable outlets or diaphragms. Another type is the pyrotechnic gas generator wherein a propellant is ignited and the resultant gas flows through an outlet into the cushion. A third type is the hybrid or augmented type. This type includes a pressure vessel containing stored pressurized gas and a pyrotechnic heater. When the heater is ignited, the stored gas from the pressure vessel is heated (expands) resulting in a greater gas volume to the airbag cushion.
All of these inflator types can be configured as dual stage inflators. Using two separate initiators, the cushion can be inflated to a low pressure at a relatively low rate under some deployment conditions; and to a higher pressure at a relatively high rate under other deployment conditions. This can be accomplished, for example, in a hybrid type inflator by providing the pressure vessel with two separately ignitable heaters.